Waves and coastal processes

Waves

Waves are made by wind blowing over the sea. The stronger the wind, the longer it blows, and the longer the (the distance of open water it blows over), the bigger the waves.


Shape	Low and long	High and steep
How often	Few a minute	Many a minute
	Strong swash, weak backwash	Weak swash, strong backwash
Effect	Build up the beach	Erode the beach

The is the water rushing up the beach; the backwash is the water draining back.

Key terms

Weathering and mass movement

Weathering breaks rock down where it is, without moving it:

Mechanical: freeze-thaw. Water in a crack freezes and expands by about 9%, widening the crack. Repeated freezing and thawing breaks the rock apart.
Rainwater is a weak acid, which slowly dissolves limestone and chalk.

is the downhill movement of material under gravity:

Sliding: a mass of rock or soil slides down a slope in one piece.
Slumping: soft rock such as clay, soaked by rain, slips down a curved surface, leaving steps in the cliff.
Rock falls: pieces of rock break off a steep cliff and fall.

Key terms

Erosion

Waves erode the coast, wearing it away, in three ways:

waves crash into the cliff and force air and water into cracks, putting the rock under great pressure and breaking it apart.
waves hurl sand and pebbles at the cliff, scraping and wearing it away, like sandpaper.
Attrition: rocks and pebbles knock against each other, becoming smaller and rounder.

Common mistake

Weathering breaks rock down where it is; erosion wears it away and carries it off, here by the sea.

Key terms

Longshore drift and deposition

moves sand and shingle along the coast:

The drives waves onto the beach at an angle.
The carries material up the beach at the same angle.
The drags it straight back down, under gravity.
Step by step, in a zigzag, material moves along the beach.

happens when the sea loses energy and drops what it is carrying. This happens:

in and behind spits;
where bring in more than the backwash takes away;
where the coast changes direction and the drift runs into deeper, calmer water.

Key terms

Exam practice

Plan your own answer first, then open the model answers to see what each level looks like.

6 marks · about 6 minutes

Explain how longshore drift and deposition shape a coastline.

Explain means: Give the reasons why something happens, developing each point with "because" or "so".

Level 1 (Basic)· 2/6 marks (band 1–2)

Longshore drift moves sand along the beach. It is deposited in bays.

Why this level: Two correct ideas, but the process isn't explained. To reach Level 2: explain how swash and backwash move material, and why deposition happens.

Level 2 (Clear)· 4/6 marks (band 3–4)

Waves approach the beach at an angle because of the prevailing wind. The swash carries sand up the beach at an angle, and the backwash pulls it straight back down, so it moves along the coast in a zigzag. Where the sea loses energy, such as in a sheltered bay, it deposits the sand, forming a beach.

Why this level: Clear explanation of longshore drift and deposition. To reach Level 3: develop where and why deposition happens, and explain how it builds landforms such as spits.

Level 3 (Detailed)· 6/6 marks (band 5–6)

The prevailing wind drives waves onto the beach at an angle. The swash carries sand and shingle up the beach at that angle, and the backwash drags it straight back down the slope, under gravity. Repeated many times, this moves material along the coast in a zigzag: longshore drift. Where the sea loses energy, such as in sheltered bays, in the lee of headlands, or where the coast changes direction into calmer water, the waves can no longer carry the material, so they deposit it. This builds wide sandy beaches in bays, and where the coast changes direction, material is carried out into the sea, building spits, such as at the mouth of an estuary.

Why this level: Detailed, step-by-step explanation of the process and where deposition happens, linked to the landforms it creates. This is Level 3.

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